Plastic materials, particularly polyester materials, are being used more and more in applications such as architectural windows, viewing media, glazing media, as well as in automotive glazing products. Their superior optical clarity, and relatively low cost make them attractive, suitable, and preferred for such applications.
A drawback of polyester films and fibers is their susceptibility to damage by ultraviolet radiation, particularly over the long periods of exposure that these applications normally require Accordingly, several methods have been tried in the past to improve the stability of polyester products to ultraviolet radiation. These methods generally revolve around using an additive or a coating that absorbs in the ultraviolet region, with negligible absorption in the visible region. Such a selective absorption would improve ultraviolet stability, but will not reduce optical clarity of the polyester products significantly.
Some additives that are used as ultraviolet protecting agents are described by D. A. Gordon in "Light Stablilizers", Encyclopedia of Basic Materials for Plastics, H. R. Simonds and J. M. Church Eds., Reinhold, New York, 1967. The disadvantages with the use of additives include high levels of concentration needed for adequate protection, uneven distribution of the additives in the polymer, potential migration, and low level of protection offered. Therefore, generally polymeric materials that can form clear coatings and also absorb ultraviolet radiation are preferred in the industry.
Polymeric coatings based on main chain aromatic polyesters are described by S. M. Cohen et al, "Transparent Ultraviolet-barrier Coatings", Journal of Polymer Science, Part A-1, Volume 9, pages 3263-3299 (1971). These main chain polyesters, upon ultraviolet radiation, undergo photo-Fried rearrangement to provide polymeric o-hydroxybenzophenones, as described below: ##STR1## Several of these main chain polyesters are commercially available, some of them under the term polyarylates, such as, for example, the Durel.RTM. polyarylate resin (sold by Hoechst Celanese Corporation, Engineering Resins Division, Chatham, N.J.). Such main chain polyesters produce benzophenones on photo-Fries rearrangement as the equation above shows. Benzophenones and benzophenone derivatives are excellent ultraviolet screens. Unfortunately, such main chain aromatic polyesters have poor solubility in common organic solvents, especially solvents of low toxicity, and no dispersibility in aqueous solvent systems.
Accordingly, it is an object of this invention to provide polymeric compositions that have very good solubility in common organic solvents as well as dispersibility in aqueous solvent systems.
A further object is to provide coatings for plastic products, particularly for polyester films, textiles, and the like, the coatings offering excellent protection to the underlying polyester.
Yet another object is to provide coatings that maintain the clarity and transparency of polyester films, while at the same time offering excellent stability toward ultraviolet radiation.
These and other objects as well as the advantages of the present invention shall become apparent from the accompanying description, examples and claims.